His form prompted manager Ian Hendon to offer him a one-year deal at Underhill and Harrison fully expects the well-travelled hitman to sign.
"I think he will," he said. "He lives locally anyway. The fact that he played our last 20 games of the season has made his mind up and living 15 minutes from the ground is another plus factor for him.
"He looks after himself so well. We'd seen him a few times last season and knew what he was all about. We took him on loan for a month and it was a bit of a risk but we knew if it didn't work out we could look elsewhere. The transformation he brought to the side was unreal."
Furlong is expected to inform Hendon of his decision later this month, while Hendon, who is also chasing QPR goalkeeper Jake Cole, has ruled out making a move for former loanee Abu Ogogo who has left Arsenal.